Power transistors carry high currents that can damage semiconductor devices, reducing reliability. The efficiency and reliability of a power transistor may be limited by the Metal-Oxide-Semiconductor Field-Effect Transistor (MOSFET) channel and the body diode. Compound substrates such as Silicon Carbide (SiC) or Gallium Nitride (GaN) can yield higher efficiency and more reliable devices compared with traditional Silicon (Si) substrates.
However, the electron mobility in a SiC channel is lower than that for a Silicon channel, causing higher channel conduction losses in SiC devices. The higher forward voltage of the SiC body diode also can cause higher conduction losses. Body diodes have bi-polar currents, so there is a time delay during switching, resulting in a switching loss. Degradation can increase drift region resistance over time, reducing reliability of the body diode. Charge can be trapped in the interface between the SiC channel and the gate oxide, shifting the threshold voltage over time.
What is desired is a power transistor constructed on a Silicon-Carbide (SiC) substrate. A heterojunction device is desired that has a Silicon channel over a SiC substrate to reduce charge trapped at the gate oxide interface, and for increased mobility. A Schottky diode is desired to provide uni-polar rather than bi-polar current to reduce switching losses and improve reliability. Buried shielding is desired to reduce electric field crowding near the Schottky diode and the heterojunction gate. A shielded, integrated, Schottky diode, heterojunction Silicon-Carbide device is desired.